This invention relates to nuts which may be ^■ * tfireadedly engaged with bolts, studs or the like to form part of or to secure a security installation, closure or the like. 5 In the past, nuts have often been a weak link in security because with the right spanner or a suitable wrench a miscreant has been able to breach the security. There have been examples of cash boxes bolted to the floor of commercial vehicles by headless bolts. 10 Secure enough from inside the vehicle, but all a thief has to do is to undo the corresponding nuts from beneath the vehicle and remove the bolts and make off with the box. One attempt to prevent the removal of nuts are the key lockable nuts sometimes 15 used to prevent the theft of wheels from automobiles. These however are expensive for regular security use and are in any case not too difficult to breach. What is required is a nut which once tightened can be made permanently irremovable from its threaded 20 shank, and" the object of this invention is to provide such a nut.

According to the invention there is provided a security nut comprising a body portion having a central shank receiving threaded bore therein, and 25 a tightening tool engageable head portion connected to the body portion by a readily frangible torque transmittable intermediate portion, wherein a rotatable collar is provided around the body portion. Thus the nut may be tightened in the usual way by engaging 30 a tightening tool with the head portion. Tightening torque is transmitted to the body portion by the intermediate portion, and once the required tightness is achieved the head portion may be snapped, cut

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- 2 - or otherwise broken off leaving only the body portion and rotatable collar remaining. Since the collar is rotatable no purchase is afforded to an intending remover making it permanently extremely difficult if not impossible to remove the nut. Any purchase tfiat may be effected by e.g. a wrench engaged on the collar can only result in the futile spinning of the collar around the body portion which remains firmly irremovable. Ball or roller bearings, or other friction reducing means such a grease packed fibre washers may be provided between collar and main body to reduce friction while supporting the collar against deformation. In a preferred emodiment the body portion and rotable. collar are annular. The intermediate frangible portion could comprise a plurality of integral bridges between the other two portions, but I provide preferably a reduced diameter neck of sufficient strength to transmit the tightening torque, yet readily rupturable by for example a saw blade or a blow from a cold chisel. In order that the invention may be readily understood an embodiment thereof will now be described by way of example with reference to the accompanying drawing which shows a section through a nut of the invention.

The nut comprises an annular body portion 1 connected to a hexagonal sided head portion 2 by a reduced diameter neck portion 3. The body portion has a central threaded bore 4 for receiving the shank of a bolt or stud and the head portion is formed with a coaxial bore 5 of somewhat greater diameter to allow removal of the head portion from the exposed end if any of the shank.

Around the main body is disposed a rotatable collar 6 of hardened steel retained thereon by an inwardly directed flange 7. This flange engages in an annular ledge 8 whose axial depth is greater

- 3 - than the axial thickness of the flange 7 to permit ready rotation. A metal washer 9 is provided to prevent the inner end 10 of the nut penetrating the abutting for example wooden surface and causing the collar to foul therewith.

.' In use the nut is tightened up in the configuration shown and then the head portion 2 is removed by cutting or other fracture of the intermediate portion 3 to leave only the rotable collar clad body portion exposed

10 which cannot be rotated by a tool and is therefore irremovable and secure.

A